In the automobile industry, or the machinery industry, there has been an increased demand for sensors capable of precisely detecting a physical quantity such as force, acceleration or magnetism. Particularly, miniaturized sensors capable of detecting such physical quantities every respective components in two-dimensional or three-dimensional directions are desired.
In order to cope with such demand, there has been proposed a force sensor in which gauge resistors are formed on a substrate made of semiconductor such as silicon, etc. to transform a mechanical distortion produced in the substrate on the basis of a force applied from the external to an electric signal by making use of a piezo resistance effect. If a weight body is attached to the detecting portion of this force sensor, an acceleration sensor for detecting an acceleration applied to the weight body can be realized. Further, if a magnetic body is attached thereto, a magnetic sensor for detecting a magnetism applied to a magnetic body can be realized. For example, sensors based on the above-described principle are disclosed in International Publications No. WO88/08521 and No. WO89/02587 based on the Patent Cooperation Treaty.
Further, in a Japanese Patent Application No. 274299/1990, a sensor utilizing a change in electrostatic capacity between two electrodes, and a sensor of a structure including a piezoelectric element put between two electrode plates are disclosed. These sensors allow a spacing or interval between two electrode plates to be varied by an action of force, acceleration or magnetism, etc., thus to detect a change in the interval as a change of an electrostatic capacitance, or a change of a quantity of charges produced in the piezoelectric element.
Generally, since a gauge resistor or a piezo resistance element has a temperature dependency, in the above-described sensor using semiconductor substrate, if there occurs a change in temperature of an environment where it is used, a detected value will include an error. Accordingly, in order to carry out a precise measurement, it is necessary to carry out a temperature compensation. Particularly, in the case where such a sensor is used in the field such as an automotive vehicle, etc., a temperature compensation is required with respect to a relatively broad operating temperature range of -40.degree. to +120.degree. C.
Furthermore, the above-described sensor utilizing a change of electrostatic capacitance has a merit that a manufacturing cost is low, but a drawback that signal processing is difficult because an electrostatic capacitance formed is small. In addition, the conventionally proposed sensor utilizing piezoelectric element has a problem that there is difficulty in manufacturing because it is necessary to put a piezoelectric element between electrodes.
With the above in view, an object of this invention is to provide a sensor for force, acceleration or magnetism, which is capable of carrying out a high precision detection without temperature compensation, and which can be easily manufactured.